1. Field of the Invention
The present invention relates to the use of hydrophobins for preventing the formation of ice on surfaces, especially to the prevention of ice formation on hard surfaces.
2. Description of Related Art
Ice formation on surfaces, for example the surfaces of aircraft or motor vehicles, can lead to considerable safety problems, and, in the extreme case, an icebound aircraft or motor vehicle can no longer be operated. Ice formation on surfaces can also lead to undesired changes in the properties of the components in question. For example, in the case of a wind turbine, the aerodynamic properties of the wind turbine can be changed by ice formation. Various techniques are therefore known for eliminating ice layers or for preventing ice formation on surfaces.
Deicing in the actual sense is understood to mean the operation of actively freeing a surface of a snow or ice layer which is already present. This includes techniques such as the simple mechanical scraping of the ice from the surface with a suitable tool. Since this is of course not possible in the case of an aircraft during a flight, many aircraft are equipped with so-called “boots”. These are rubber hoses which are placed on particularly endangered sites on the aircraft, for example the front edges of the wings, the aerofoils or the rudder, and which can be blown up if required in order to remove the ice in an explosive manner. Further details on this subject are disclosed, for example, by GB 1,166,526 or WO 02/42150. In addition, ice can be melted by waste heat from the engines which has been diverted through pipe systems, as disclosed, for example, by U.S. Pat. No. 6,267,328. However, this method is only possible in the case of relatively large aircraft and is additionally becoming increasingly inefficient, since the engines of modern aircraft are becoming ever more energy-efficient and produce less waste heat. In addition, thermoelectric heating films can be placed at particularly endangered sites (GB 787954).
It is also known to use chemicals for deicing. Typical icing fluids consist generally of water and particular proportions of ethylene glycol and/or propylene glycol. Reference is made by way of example to GB 2,050,398, WO 00/00568 or WO 07/104,996. The deicing fluid brings about a freezing point depression and thus frees the surface of the ice. In flight, deicing fluid can be sprayed out of holes in the aerofoils. U.S. Pat. No. 6,861,009 discloses compositions for deicing which comprise proteins. What is proposed is in particular the use of proteins which are ubiquitous in agriculture or cattle husbandry.
In addition to the active deicing of already iced surfaces, techniques have also been proposed with which ice formation on a surface is to be prevented from the start (anti-icing), such that subsequent deicing is no longer necessary.
For this purpose, for example, the surface can be provided with ice-preventing coatings. In aviation, it is possible for this purpose to use, for example, freezing point-depressing coatings, which consist of thickened mixtures of ethylene glycol and/or propylene glycol with water. The adhesive forces of these coatings are, however, so weak that they have flowed off the aerofoils of an aircraft within a few minutes up to a maximum of a few hours and thus do not offer any further protection from icing.
In addition, hydrophobic coatings for preventing ice formation are known. For example, JP-A 60-208373 discloses a composition for coating, which comprises methylsiloxane, acryloyl glycidyl ether, a thickener based on silicone, an epoxy resin, Teflon powder and fluorophosphoric esters. U.S. Pat. No. 6,702,953 discloses a coating produced in a sol-gel process, which consists of a hydrophobic matrix and a multicomponent freezing point depressant. The freezing point depressant consists of an alkoxide precursor which brings about slow emergence of a polyol to the surface of the coating.
Hydrophobins are small proteins of from about 100 to 150 amino acids, which occur in filamentous fungi, for example Schizophyllum commune. They generally have 8 cysteine units. Hydrophobins can be isolated from natural sources, but can also be obtained by recombinant methods, as disclosed, for example, by WO 2006/082251 or WO 2006/131564.
The prior art has proposed the use of hydrophobins for various applications.
WO 96/41882 proposes the use of hydrophobins as emulsifiers, thickeners, surfactants, for hydrophilizing hydrophobic surfaces, for improving the water stability of hydrophilic substrates, for preparing oil-in-water emulsions or water-in-oil emulsions. Additionally proposed are pharmaceutical applications such as the production of ointments or creams, and cosmetic applications such as skin protection or the production of shampoos or hair rinses. EP 1 252 516 discloses the coating of various substrates with a solution comprising hydrophobins at a temperature of from 30 to 80° C. WO 2006/082253 discloses the coating of surfaces with fusion hydrophobins at a pH of ≧4.
US 2006 0024417 discloses air-filled or foamed foods, for example ice cream or mousse, which comprise a hydrophobin. US 2006 0024419 discloses a frozen composition, for example foods, which comprise hydrophobins. It further discloses a process for inhibiting the growth of ice crystals in frozen products, in which a hydrophobin is added to the product to be frozen or during the freezing. In both cases, preference is given in each case to using class II hydrophobins. In contrast to class I hydrophobins, class II hydrophobins are readily soluble.
The use of hydrophobins for preventing ice formation on surfaces is to date still unknown.